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You are provided with:
| labelled | contents | hazard | volume /cm3 |
|---|---|---|---|
| E | invertase solution | irritant | 15 |
| S | sucrose solution | none | 15 |
| Benedict’s solution | Benedict’s solution | harmful irritant | 60 |
| W | distilled water | none | 200 |
• V, one length of Visking (dialysis) tubing in distilled water.
You will need to run the time course for the enzyme-catalysed reaction for 20 minutes.
Fig. 1.1 shows the procedure for investigating the time course of the enzyme-catalysed reaction. The times you will use are 5 minutes, 10 minutes, 15 minutes and 20 minutes.
Proceed as follows:
1. Label the large test-tubes with the times and put 30 cm3 of distilled water into each one.
2. While you are doing steps 3 to 16 you will need to heat up the beaker of water labelled for Benedict’s test so that it can be used later to carry out the Benedict’s test.
Decide on the temperature you plan to use for this water-bath.
(i) State the temperature you have chosen in the space below. .................................................. °C [1]
3. Prepare a water-bath between 35 °C and 40 °C using the beaker of water labelled for reaction.
4. Put all the labelled large test-tubes into the water-bath labelled for reaction.
5. Tie a knot in the Visking tubing as close as possible to one end so that it seals the end forming a bag.
6. To open the other end, wet the Visking tubing and rub the tubing gently between your fingers.
7. Put 4 cm3 of S into the open end of the bag.
8. Put the bag into the water in the first large unlabelled test-tube.
9. Allow 3 minutes for S in the bag to reach the same temperature as the distilled water surrounding the bag.
10. Put 4 cm3 of enzyme E into the bag. You need to mix the enzyme with the substrate. Remove the bag, close the open end between your fingers. Holding both ends tightly, turn the bag upside down several times and this will mix the contents.
11. Put the bag back into the second large test-tube, labelled 5. Start timing the time course.
12. After 5 minutes remove the bag and contents and place it into the next large test-tube.
13. Repeat step 12 as shown in Fig. 1.1.
14. After 20 minutes, put your bag with its contents into the container labelled for waste.
15. At the end of the 20 minutes put the contents of each large test-tube into separate labelled small containers.
16. Test the contents of the small containers for reducing sugars using Benedict’s solution. You will need to keep the volume of Benedict’s solution the same for each test.
Decide on the volume of sampling solution and Benedict’s solution you plan to use for each test.
(ii) State the volume of sampling solution and Benedict’s solution you have chosen.
volume of sampling solution ............................................................
volume of Benedict’s solution .......................................................... [2]
17. In the small test-tubes, add the volumes of samples and Benedict’s given in (ii).
18. Put all the test-tubes into the water-bath for Benedict’s test and immediately start timing.
19. Record the time for the change from blue to the first colour you see (ignore any further colour changes). If there is no colour change at 10 minutes, record “more than 600”.
(iii) Prepare the space below and record your results. [4]
(iv) Identify one significant source of error in this investigation. ............................................................. ............................................................. [1]
(v) Describe a suitable control for this investigation. ............................................................ ............................................................ [1]
(vi) Suggest how you would make two improvements to this investigation. ................................................ ................................................ ................................................ ................................................ [2]
(b) A student investigated the effect of placing pieces of tissue from a potato in sucrose solutions of different concentrations. At the start, each sample of potato tissue was weighed and the initial mass was recorded. Then each sample of potato tissue was placed into a different concentration of sucrose solution. After a set time the potato tissue was removed and the final mass of the potato tissue was recorded. The change in mass and percentage change of mass for each sample of potato tissue was calculated. The results of the student’s investigation are shown in Table 1.1.
[Table_1]
(i) Complete Table 1.1. [1]
(ii) Plot a graph of the data shown in Table 1.1. [4]
(iii) Draw a circle around the anomalous result on the graph. [1]
(iv) Complete Table 1.2 below.
[Table_2]
(v) Explain, in terms of water potential, the movement of water in cell A. [2]
500
551
596
L1 is a slide of a stained transverse section through a plant leaf. The plant belongs to a genus which grows widely especially in Chile and Argentina.
Fig. 2.1
(a) (i) Draw a large plan diagram of the part of the leaf indicated by the shaded area in Fig. 2.1. Label the palisade mesophyll and the epidermis. [6]
(ii) Between the vascular bundles are openings (canals) surrounded by a wall of cells.
Make a large drawing of six adjacent (touching) cells making up this wall of cells (the inner wall of the canal). Label with the letter F a stained feature inside one cell. [6]
(iii) State one observable feature of the epidermis that supports the conclusion that this is a leaf from a plant growing in a dry habitat. Suggest how this feature helps the plant to survive in a dry habitat. ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ [1]
Fig. 2.2 is a photomicrograph of a transverse section through a leaf of a different plant species. This plant is native to Europe, North Africa and Asia but grows widely throughout the world.
Fig. 2.2
(b) Prepare the space below so that it is suitable for you to record three observable differences between the specimen on L1 and in Fig. 2.2.
Record your observations in the space you have prepared. [5]
552
535
504
